Bobbing is technically cutting the frame shorter. I'd use a M931 and not cut it. Then you have a really nice pintle hitch ready to go + air brake control for a trailer. M105 beds look good on them. I do like the 4x4, reducing weight, drag and cost of 2 tires. And the 5 ton can cruise at highway speed. Air ride would be nice too. That said, I've had several 5 ton that it could have been done to and I couldn't pull the trigger. My 4x4 project is an M35A3.
Edit....If I recall, you are working with an early version 5 ton, not the later M939 series....right?
I still like the 4x4 idea....I'm not politically correct however.